1. Field of the Invention
The invention relates to optical data storage medium accessing, and more particularly to reading of optical data storage medium by referencing specifications of the optical data storage medium.
2. Description of the Related Art
A lot of basic information for accessing an optical disc is recorded on a lead-in area or lead-out area of the optical disc. The basic information is referred to as disc fundamental information. The format and structure of disc fundamental information is defined by the physical specification of optical disc. When the optical disc is inserted into an optical drive, the optical drive must first read the lead-in area or lead-out area to obtain the disc fundamental information. The optical drive can then identify the layout of user data and access the optical disc according to the disc fundamental information. In case of BD-RE, the content of DDS and DFL in DMA area is disc fundamental information. If reading the disc fundamental information has errors, the optical drive cannot identify the layout of user data and access the optical disc correctly, and a disc mount failure is reported to host or a user.
To resist the interference of channel noise or external noise, the user data of optical disc is added with a plurality non-user data called “Parity Byte” generated by Reed-Solomon code algorithm. Several user byte data in one sector and its parity byte form one unit called “RS codeword”. Normally, one sector data has a plurality of RS codewords according to the physical specification of optical disc. The ECC decoder of optical drive could perform error correction codeword by codeword to correct the error resulting from noise and to improve correctness of user sector data. Beside that, in order to confirm reliability of user data sector, EDC (Error detection code) is also recorded with one sector data. Normally, the EDC value is following immediately after the user data in one sector. No matter whether error correction is performed or not, the EDC detector of optical drive could perform error detection to confirm reliability of user data in one sector.
For BD-RE disc, the disc fundamental information includes DDS (Disc Definition Structure) and DFL (Defect List). The area for storing DDS and DLS is called DMA (Disc Management Area). Normally, the optical drive must first read DDS sector and DFL sectors in BD-RE disc successfully, then the drive could identify the data layout of disc and mount this optical disc. The DDS sectors and DFL sectors, as the same as fore-mentioned structure of the user sector data, comprise ECC for improving correctness of user data and EDC for confirming reliability of user data. To enhance the robustness of disc accessing, the disc fundamental information is replicated to be respectively stored on different sectors of an optical disc. According to physical specification of BD-RE, there are 2 DMA in the inner ring called DMA1 and DMA2 and 2 DMA in the outer ring called DMA3 and DMA4. The contents of DMA1, DMA2, DMA3 and DMA4 are the same logically in normal case (i.e. DDS and DFL of 4 DMA have the same content in normal case).
In the conventional method, no matter error correction is performed or not, if calculated EDC value of DDS sector does not match the recorded EDC value stored in the optical disc, reading of the DDS sector is determined to have failed, and no correct disc fundamental information is generated as a basis for accessing the optical disc. In such a situation, the user data recorded in the optical disc cannot be read because of no correct information of disc layout. It is therefore a need to improve the probability of successful disc mounting for the optical discs having defects.